/Engine/Plugins/Editor/ObjectMixer/ObjectMixer/Source/ObjectMixer/Public/Views/List/Modes/ObjectMixerOutlinerHierarchy.h
Create a linearization of all direct and indirect children of a given item in the hierarchy
virtual void CreateChildren ( const FSceneOutlinerTreeItemPtr & Item, [TArray](API\Runtime\Core\Containers\TArray)< FSceneOutlinerTreeItemPtr > & OutChildren ) const